A worm known as TheMoon has been in the news recently but the actual infection of Linksys routers has likely been spreading for quite a while now. You may have also read about the backdoor on Linksys/Cisco and Netgear routers which as been open for almost a decade and can be as simple as connecting to port 8083 if you can get direct access to the router. Some of these vulnerabilities can be mitigated by turning off remote administration and uPNP services but it seems your consumer level router is still a huge security risk. Your best bet is to spend a weekend and follow the advice of most Slashdot commentators; flash your router with OpenWRT or a version of Tomato and you will have better security and control over your router. Just don't do it to the modem your ISP provided you with.

"The remote-access management flaw that allowed TheMoon worm to thrive on Linksys routers is far from the only vulnerability in that particular brand of hardware, though it might be simpler to call all home-based wireless routers gaping holes of insecurity than to list all the flaws in those of just one vendor. An even longer list of Linksys (and Cisco and Netgear) routers were identified in January as having a backdoor built into the original versions of their firmware in 2005 and never taken out."